The invention described herein was made in the course of work supported by a grant from the Department of Health, Education and Welfare, Public Health Service.
1. Field of the Invention
The present invention relates to vaccines and more particularly to antigenic gene products produced by microbes containing one or more recombinant genes from a pathogenic organism as a vaccine against the pathogenic organism.
2. Description of the Prior Art
Microbial infectious diseases are ubiquitous, although improved public health and the availability of antibiotics have decreased the incidence and minimized the consequences of infectious microbial diseases in the world. In many underdeveloped countries, however, microbial diseases are still rampant. Even in medically advanced countries, bacterial transposons that carry drug-resistance genes and numerous methods for dissemination of drug-resistance plasmids have resulted in drug resistance that has compromised the effectiveness of conventional methods of infectious disease control designed to counteract the effects of infection after infection has occurred. Thus, in the last several years, there has been increased emphasis on the development of vaccines that might prevent, if not eliminate, some infectious diseases.
Since the intact surface of a healthy epidermis is rarely, if ever, penetrated by microbes, the point of initial infection is most often one of the mucous membranes. These include the conjunctiva and the oral, respiratory, gastrointestinal and genitourinary surfaces. The mucous secretions of these membranes as well as the secretions from tear, salivary and mammary glands can contain antibodies against invading pathogens and thus act as a first line of defense against invasive microbes. Enhancing the immune response of the secretory system is thus a desirable goal in inducing immunity against microbial pathogens such as bacteria, viruses, fungi, parasites, etc.
Previously used vaccines against bacterial diseases have generally comprised (I) specific components purified from the etiologic agents, (II) the whole killed etiologic agent, or (III) an avirulent derivative of the etiologic agent as a live vaccine. Numerous vaccines of these three types exist, of which the following are selected examples:
U.S. Pat. No. 4,250,262, discloses methods for recovering the enzyme glucosyltransferase from Streptococcus mutans and the use of this purified enzyme in local immunization against dental caries, a Type I vaccine. Details for culturing the bacteria, purifying the enzyme, and using the enzyme to stimulate IgA antibody in saliva are presented for serotype a, c or g of S. mutans. Other examples of vaccines from purified specific components of bacteria are found in U.S. Pat. Nos. 4,203,971 and 3,239,749, which disclose a vaccine useful against infection by Neisseria gonorrhoeae which consists of a glycoprotein from the outer coat material of gonococci. Injection of the glycoprotein stimulates a bactericidal antibody.
The use of dead S. mutans cells to immunize against tooth decay via administering in the mouth, which is disclosed in U.S. Pat. No. 3,931,398, is an example of a Type II vaccine. The inventors recognized that immunoglobulin A (IgA) antibodies were the antibodies being produced and that they resulted in a decrease in plaque formation.
A live bacterial vaccine (Type III) which contains selected strains of Escherichia coli bacteria is disclosed in U.S. Pat. No. 3,975,517. The bacteria were treated with dilute formalin to attenuate or partially inactivate them before injection into the mammary gland of a sow. Antibody thereby produced was later found in the milk and protected newborn swine against E. coli infections. The formalin treatment that caused the E. coli inactivation was only a temporary attenuation of the bacteria and care had to be taken to prevent bacterial recovery before injection. Such recovery would have resulted in serious infection rather than protection.
Another example of a Type III vaccine is described by Germanier et al. in U.S. Pat. No. 3,856,935 wherein a live S. typhi Ty21a derivative is employed as an oral vaccine against typhoid infection.
Several problems exist in producing vaccines directly from pathogenic organisms, as indicated in the E. coli (Type III) example above. In addition, a principle obstacle to using whole bacteria (living or killed) or impure preparations obtained from the pathogenic bacteria is the presence of antigenic substances in such preparations that may cause undesirable cross reaction. For example, protein antigens produced by S. mutans have been reported to cross-react with antigens present in human heart muscle and thus, like other pathogenic bacterial proteins, may pose a problem of safety when used in a vaccine for humans.
Other problems arise in developing a vaccine capable of oral administration, certainly the most desirable form of administration when considered in terms of either widespread use by unskilled administrators in underdeveloped countries or in terms of patient comfort and acceptability. When oral administration is used to stimulate a secretory IgA (sIgA) response, the amount of material that is actually absorbed and capable of stimulating an effective immune response is usually low. The dose of antigen required for oral immunization generally far exceeds that required for systemic induction of humoral immunity (IgG). It is assumed that a large portion of the antigen is degraded by enzymes of the gastrointestinal tract and may be eliminated or absorbed in a nonimmunogenic form.